The influences of combined pollution of Pb2+ and Cd2+ on soil nitrifying activity after 45 days
incubation was listed in Table 3. Disagree with that on soil urease activity, the inhibition effect was
appeared in all these amendments including the lower concentration, such as the 0.5 mg/kg Cd2+ only
treatment and 0.5 mg/kg Pb2+ and 0.5 mg/kg Cd2+ combined. In comparison with the control, soil
nitrifying activity in soil contaminated with 0.5 mg/kg Cd2+ was found to be 79.23 ± 4.20 %, lower than
the control 83.12% ± 4.16 %. The relative inhibition was increased with the increasing of Pb2+
concentration. When the content of Pb2+ increased from 0.5 mg/kg to 100.0 mg/kg combined with the
constant concentration of 0.5 mg/kg Cd2+, the relative inhibition increased from 4.7 % to 47.6 %.